In two lactation studies reported in this dissertation, it was hypothesized that feeding 35% brown midrib corn silage (BMRCS) and 25% alfalfa hay (dry matter basis) would result in increased dry matter intake (DMI) around peak lactation compared with feeding conventional corn silage (CCS), causing longer peak milk production, and that feeding dairy cows in early lactation a 16% crude protein diet with fair quality alfalfa hay (FAH) in BMR-based diets would maintain milk production, reduce urinary N excretion, and improve N efficiency compared to those fed high quality alfalfa hay (HAH) in CCS- or BMR-based diets. A third experiment was conducted to assess in situ degradation kinetics of BMRCS harvested prior to or at maturity. The first lactation study was performed to determine the long-term effects of feeding BMRCS fed with a high dietary concentration of good quality alfalfa hay in a high-forage lactation diet on productive performance of Holstein dairy cows for the first 180 d of lactation. Feeding BMRCS-based diet did not affect milk production through peak lactation compared with a CCS-based diet; however, cows fed the BMRCS-based diet maintained heavier body weight through peak lactation and longer peak milk production, which resulted in increased milk yield post peak lactation, leading to greater overall milk production and milk protein yield. A second lactation experiment was performed to investigate if early lactating dairy cows fed with the FAH in BMRCS-based diets would reduce urinary N excretion and improve N efficiency compared to those fed the HAH in CCS- or BMR-based diets. Feeding BMR and HAH had better N utilization by decreasing concentrations of urea in blood, milk, and urine. In addition, feeding BMR-based diets decreased urinary N-to-fecal N ratio, and it was further reduced by feeding the HAH, which can represent an environmental advantage over traditional sources of forages in lactation dairy diets. A third experiment assessed in situ DM and neutral detergent fiber degradation kinetics for two new pre-matured BMR varieties (pmBMR1 and pmBMR2) that can be double-cropped by harvesting at tassel, compared with a sole crop mature BMR (mBMR) and CCS harvested at maturity in dry and lactating Holstein dairy cows. The potentially degradable NDF fraction was greater for BMR hybrids compared with CCS with the exception of the pmBMR2, which had the lowest potentially degradable NDF fraction in dry cows. Estimates of ruminal degradability of NDF were greatest for pmBMR1 in both dry and lactating cows. Feeding BMRCS exerted nutritive and environmental benefits when fed with typical Intermountain West lactation dairy diets. Further research is needed to understand interactive aspects of nutrient utilization with other dietary ingredients under different physiological conditions to take full potential benefits of BMRCS.

This experiment was conducted to determine the effects of corn silage hybrids and nonforage fiber sources (NFFS) in high forage diets formulated with high dietary proportion of alfalfa hay (AH) and corn silage (CS) on ruminal fermentation and productive performance by early lactating dairy cows. Eight multiparous Holstein cows (4 ruminally fistulated) averaging 36 ± 6.2 d in milk were used in a duplicated 4 × 4 Latin square design experiment with a 2 × 2 factorial arrangement of treatments. Cows were fed 1 of 4 dietary treatments during each of the four 21-d periods. Treatments were: 1) conventional corn silage (CCS)-based diet without NFFS, 2) CCS-based diet with NFFS, 3) brown midrib corn silage (BMRCS)-based diet without NFFS, and 4) BMRCS-based diet with NFFS. Diets were isonitrogenous and isocaloric. Sources of NFFS consisted of ground soyhulls and pelleted beet pulp to replace a portion of AH and CS in the diets. In vitro 30-h NDF degradability was greater for BRMCS than CCS (42.3 vs. 31.2%). Neither CS hybrids nor NFFS affected intake of DM and nutrients. Digestibility of N, NDF, and ADF tended to be greater for cows consuming CCS-based diets. Milk yield was not influenced by CS hybrids and NFFS. However, a tendency for an interaction between CS hybrids and NFFS occurred with increasing milk yield due to feeding NFFS with the BMRCS-based diets. Yields of milk fat and 3.5% FCM decreased when feeding the BMRCS-based diet, and there was a tendency for an interaction between CS hybrids and NFFS by further decreased milk fat concentration because of feeding NFFS with BMRCS-based diet. Although feed efficiency (milk/DM intake) was not affected by corn silage hybrids and NFFS, there was an interaction between CS hybrids and NFFS because feed efficiency increased when NFFS was fed only with BMRCS-based diet. Total VFA production and individual molar proportion were not affected by diets. Dietary treatments did not influence ruminal pH profiles except that duration (h/d) of pH < 5.8 decreased when NFFS was fed in CCS-based diet but not in a BMRCS-based diet, causing a tendency for an interaction between CS hybrids and NFFS. Overall measurements in our study reveal that high forage NDF concentration (20% DM on average) may eliminate potentially positive effects of BMRCS. In the high forage diets, NFFS exerted limited effects on productive performance when they replaced AH and CS. Although the high quality AH provided adequate NDF (38.3% DM) for optimal rumen fermentative function, the low NDF concentration of the AH and the overall forage particle size reduced physically effective fiber and milk fat concentration.

Developing solutions to the metabolic stress experienced by cows during the transition period is very important because it can negatively influence lactational performance. The objectives were to: 1) compare physiological changes through body weight (BW) and concentrations of non-esterified fatty acids (NEFA) and β-hydroxybutyric acid (BHBA) and 2) evaluate feed intake, milk production, and energy balance (EB) of cows fed brown midrib corn silage (BMRCS)-based diets when compared with conventional corn silage (CCS)-based diets during the transition. At 4 wk prior to parturition, 40 dry multiparous Holstein cows were randomly assigned treatments. The treatment groups consisted of 2 close-up transition diets (CCS-based and BMRCS-based diet) offered to 2 groups of 20 cows each beginning at 4 wk prepartum. After calving, 10 cows from each prepartum group were individually fed one of four dietary treatments. The four dietary treatments postpartum were defined as follows: 1) CC = CCS-based close-up diet + CCS-based lactation diet; 2) CB = CCS-based close-up diet + BMRCS-based lactation diet; 3) BB = BMRCS-based close-up diet + BMRCS-based lactation diet; 4) BC = BMRCS-based close-up diet + CCS-based lactation diet. Cows were sampled weekly for feed intake, and feed composition was taken monthly. After calving, milk yields were recorded daily and milk components were analyzed monthly. Body weights were taken twice per week on wk -4, -2, 1, 2, 3, 4, 8, 12, 16, and 20. Blood serum was sampled 3 times per week from wk -4 through 4 and then on wk 6, 8, 14, and 20. Rumen fluid was sampled on wk -4, 4, 8, 14, and 20. Feeding BMRCS-based diets during the transition did have a positive influence on dry matter intake, milk production, and energy balance. Interestingly, feeding BMRCS-based diets only during the close-up period and feeding a CCS-based diet during the lactation had similar positive effects as feeding a BMRCS-based diet through the dry period and during the lactation. This finding is meaningful because producers, especially in the Intermountain West, have experienced BMR crop yields that have been less than that of conventional crop yields and may be unwilling to utilize BMRCS in dairy rations. However, if feeding a BMRCS-based diet for a limited amount of time is beneficial, producers could be more willing to utilize this silage hybrid as an important transition period management tool.